1. Field of the Invention
The present invention relates to a wheel spindle device for mounting a plurality of grinding wheels with inclined grooves formed on grinding surfaces thereof, on a wheel spindle of a grinding machine.
2. Discussion of the Related Art
In Japanese unexamined, published patent application No. 2000-354969, there is described a grooved grinding wheel, wherein an abrasive grain layer including super abrasive grains such as, for example, diamond or cubic boron nitride (CBN) is formed on a circumferential surface of a disc-like core member drivingly rotated about an axis. Oblique or inclined grooves each having a predetermined width and a predetermined depth are formed on a grinding surface which is a circumferential surface of the abrasive grain layer, at an angle inclined in a range of 25 to 45 degrees relative to the axis of the core member. The grooved grinding wheel like this is capable of effectively leading coolant along the inclined grooves to a grinding point and hence, is capable of enhancing the grinding efficiency as a result of increasing the material removable rate to about one and half times as high as that of a grinding wheel which does not have such inclined grooves.
Further, it is generally known in the art that coolant supplied to a grinding point causes a dynamic pressure to be generated between a grinding wheel and a workpiece being ground therewith. Therefore, it is necessary to prevent the machining accuracy and the machining efficiency from being deteriorated as a result that the dynamic pressure causes the workpiece to be displaced away from the grinding wheel.
Further, Japanese unexamined, published patent application No. 2006-068856 describes a wheel spindle structure, wherein two grinding wheels are secured in a juxtaposed relation by means of a plurality of bolts with a predetermined space retained therebetween and are mounted on a wheel spindle of a wheel head. In the construction shown in the patent document, the wheel spindle is rotatably supported at opposite end portions thereof. This way of supporting the wheel spindle decreases the bending or flexing of the wheel spindle during a machining operation, so that the machining accuracy can be enhanced. In addition, the way of supporting the wheel spindle makes it possible to separate the wheel spindle in the axial direction, so that the exchange of the grinding wheels with those fresh becomes easy. Generally, the production efficiency can be improved by the use of plural grinding wheels, because it becomes possible to grind two axially spaced portions of the workpiece to the same or different shapes at a time.
However, in the prior art device described in the first mentioned Japanese application, it occurs that the number of the inclined grooves which across the grinding point area changes from one groove to two grooves and vice versa. This undesirably causes the area on the grinding surface (i.e., the area of abrasive grains of the grinding wheel which contacts the workpiece) to vary in dependence on the positions of the inclined grooves or the rotational angle of the grinding wheel, whereby change occurs in the grinding resistance. Further, it may be the case that it is difficult as practical matter to make the inclined grooves uniform in width. The lack of uniformity in the inclined grooves formed on the grinding surface likewise causes the grinding resistance to fluctuate.
In particular, where several grinding wheels each with such inclined grooves formed on the grinding surface thereof are assembled on a wheel spindle 32 in axial alignment as shown in FIG. 11, the following drawback may arise. That is, where the angular phases of the inclined grooves 20 formed on one grinding wheel 10 are in coincidence with those on the other or another grinding wheel 10, the grinding resistances on the respective grinding wheels may be synchronized to grow through a combined or synergy effect therebetween. This may undesirably results in chattering as the case may be, and may give rise to a drawback that the machining accuracy of the workpiece is deteriorated.